A winding shaft assembly and a sunroof assembly including the same are provided. The winding shaft assembly includes an inner tube, a connecting rod, two first pulleys, a spring fixing seat, a spring fixing shaft, a spring, and two winding shaft supports. The connecting rod is rotatably embedded in and passes through the inner tube. The two first pulleys are fixedly connected to the connecting rod in a rotation direction of the connecting rod. The two first pulleys are movably connected to the connecting rod in an axial direction of the connecting rod. The spring fixing seat is disposed between the inner tube and the connecting rod and fixed at one end of the inner tube. The sunroof assembly further includes a driving mechanism and a synchronous belt. The driving mechanism is connected to at least one first pulley and/or at least one second pulley.